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PCF8574 and PCF8574A I/O Expanders
Texas Instruments’ (TI) PCF8574 and PCF8574A are two-wire I
2
C-bus to
8-bit parallel bus I/O expanders from TI’s I
2
C logic portfolio. They are
designed to provide a simple and cost-effective method to monitor and
control several peripheral signals. The difference between the PCF8574
and PCF8574A is the I
2
C address:
•
PCF8574 has addresses ranging from 0x20 to 0x27 (up to
eight PCF8574 devices may be used on the same I
2
C bus).
•
The PCF8574 and PCF8574A have addresses ranging from 0x38 to
0x3F (up to eight PCF8574A devices may be used on the same I
2
C
bus).
•
A total of 16 PCF8574 and PCF8574A devices may be used
on the same I
2
C bus.
The PCF8574 and PCF8574A use the serial clock (SCL) and serial data
(SDA) I
2
C lines to communicate with the bus controller.
Key Features
•
Pin-to-pin compatible and functionally
equivalent with Philips PCF8574 and
PCF8574A (PDIP, SOIC and TSSOP)
•
In addition, TI has package offerings that
are smaller than Philips package options:
– 20-pin TVSOP (23% smaller than
20-pin TSSOP)
– 20-pin QFN package (62% smaller than
20-pin TSSOP); industry’s smallest
PCF8574 and PCF8574A package
•
Two-wire I
2
C-bus to 8-bit bidirectional
parallel-bus expander
•
Operating supply voltage from 2.5-V to
6-V V
CC
•
Low standby current consumption
of 10 mA maximum (F
SCL
=OH
Z
)
•
Open-drain interrupt output to signal a
change on an I/O pin
•
Latched outputs with high-current
drive capability for driving LEDs
•
Addressed by three hardware-address pins
•
Top applications:
– Fan control
– LED driver
– System monitoring
– Temperature sensor monitoring
– Push button monitoring
– 8-bit bidirectional expansion
10.3 mm
6.5 mm
5.0 mm
4.5 mm
10.3 mm
6.5 mm
6.4 mm
3.5 mm
1.27–mm pitch
0.65–mm pitch
0.4–mm pitch
0.5–mm pitch
16-Pin SOIC
(Philips Cross)
20-Pin TSSOP
(Philips Cross)
20-Pin TVSOP
20-Pin QFN
SDA
SCL
MSB LSB
R/W
RX-ACK
MSB
LSB RX-ACK
Start
Condition
Address Transfer
From Master to Slave
Data
Direction Bit
1 2 3-6 7 8 9
Data Transfer From Master to Slave (Write)
or Slave to Master (Read)
1 2 3-7 8 9
Stop
Condition
PCF8574/A Functional Block Diagram*
—
App Clip 9/28/04 8:58 AM Page 1
